1. Field of the Invention
The present invention relates to a correction signal generator that outputs a correction signal that corrects the linearity of an analog-to-digital (A/D) converter, and an A/D converter that corrects the linearity using the correction signal.
2. Description of the Related Art
In the related art, an A/D converter having a configuration shown in FIG. 9 is known as an A/D converter from which a high-resolution digital value is obtained by a simple configuration (see Japanese Unexamined Patent Application, First Publication No. H5-259907).
In an A/D converter 300 of FIG. 9, a pulse delay circuit 81 has a configuration in which a plurality of delay units NAND1, BUF1, . . . , BUF15 each including various gate circuits are connected in a ring shape, and an analog input signal (voltage) Vin serving as an A/D conversion target is supplied as a power supply voltage of each delay unit.
If a circulation pulse SP is input to the pulse delay circuit 81, the circulation pulse SP sequentially passes through each delay unit with a delay time corresponding to the above-described power supply voltage, and circulates within the pulse delay circuit 81.
The number of stages of delay units through which the circulation pulse SP has passed is decided by a delay time of the delay units, that is, the analog input signal Vin supplied as the power supply voltage. A pulse passage stage number detection circuit 82 detects the number of the stages (or the number of circulations).
A latch and encoder 83 receives a detection result of the pulse passage stage number detection circuit 82 at a timing when a latch pulse LP is input after a sampling time of an A/D conversion has elapsed from a start of an input of the circulation pulse SP, and outputs a value obtained by encoding the number of stages through which the circulation pulse SP has passed at the timing as a digital value Cout after the A/D conversion.
Here, because a relationship between the delay time of the delay units and the power supply voltage is not expressed by a linear function in the above-described A/D converter 300, input/output characteristics indicating a relationship between the analog input signal Vin and the digital value Cout, which is the A/D conversion result, is shown in a curve. As a method of approximating the input/output characteristics to an ideal straight line, an A/D conversion result is obtained by pre-dividing a voltage range of an analog input signal, which is an A/D conversion target, into a plurality of regions. A process of obtaining an approximation equation that connects values obtained as A/D conversion results by a straight line and correcting a digital value generated by actually performing an A/D conversion from a coordinate point obtained from the approximation equation has been proposed (see Japanese Unexamined Patent Application, First Publication No. 2004-274157).
However, there is a problem in that setting a conversion equation is complex because it is necessary to actually perform A/D conversions for a number of reference voltages, obtain A/D conversion data in coordinate points corresponding to the reference voltages, and set the conversion equation using a number of obtained A/D conversion data so as to obtain the conversion equation for approximately correcting data after the A/D conversions.